Blender Grabbing Vertices Duplicates Them
you must have duplicated your mesh, you can try 2 different things:


Select and delete the duplication: put your mouse on the mesh and press L to select the duplication, then G to move it away and X to delete.
Merge the overlapping vertices: Select the whole mesh with A and press AltM > Merge By Distance, you can see how many vertices have been deleted on the top horizontal bar, meaning there were overlapping vertices, maybe you'll have to play with the Merge Distance parameter in the operator box on the bottom left of the 3D viewport window.